A technology for managing group members has been proposed in which a common group key is provided only to the members belonging to a group. Moreover, in order to distribute a common group key to group members in a safe manner, a technology for managing group members has been proposed in which only the members belonging to a group use a group key block (GKB) enabling retrieval of the common group key. Various methods such as the Complete Subtree method and the Subset Difference method are known as the methods for creating a GKB.
A plurality of GKB creation methods is available. However, in the conventional technology, it is possible to implement only a single predetermined method, thereby resulting in a lack of flexibility.